The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-283693 filed on Sep. 18, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a collision detecting apparatus for a vehicle, which outputs a collision signal for starting a passenger protector for a vehicle, such as an air bag upon collision of the vehicle.
2. Description of Background Art
With respect to the collision detecting apparatus to which the present invention pertains, as described in Japanese Patent Laid-open No. Hei 4-176757, there is known a type including an integrating means for cumulatively integrating the output from an acceleration sensor when the output exceeds a specific calculation start level due to collision of the vehicle, wherein the collision detecting apparatus outputs a collision signal when a cumulative integral value calculated by the integrating means exceeds a specific threshold value.
The output from the acceleration sensor (detected acceleration) is rapidly changed upon collision of the vehicle. The output, however, may be sometimes periodically vary due a variety of causes other than collision during the operation of the vehicle. In this case, if the cumulative integral value of the output from the acceleration sensor exceeds the threshold value, a collision signal is uselessly outputted from the collision detecting means despite a collision of the vehicle, which requires the operation of a passenger protector, that does not occur.
For example, a motorcycle includes an acceleration sensor often mounted to a leading end portion of a front fork and its neighborhood as shown in FIG. 4 (see Japanese Patent Laid-open No. Hei 11-278342). When a front wheel rides past a stepped portion, a series of motions are applied to the leading end portion of the front fork. First, a large deceleration is applied thereto due to the contact between the front wheel and the stepped portion. Second, a large deceleration is applied thereto due to compression and bottoming of a suspension spring for the front wheel. Third, an excitation force in the vertical and longitudinal directions due to, for example, release of the compression of the suspension spring is applied thereto when the front wheel is moved upwardly. At last, a large deceleration is applied thereto when the front wheel is grounded. These series of motions cause, for example, a resonance of the front fork. As a result, the output waveform from the acceleration sensor sometimes becomes a periodical damped vibration waveform as shown in a graph of FIG. 4. The vibration waveform is characterized in that an amplitude of each of the second and later wave crests (2), (3). . . becomes larger than that of the first wave crest (1).
According to the related art collision detecting apparatus, as the amplitude of the vibration waveform of the output from the acceleration sensor becomes large (particularly, in the order of the second and later wave crests), a cumulative integral value of the output from the acceleration sensor may sometimes exceed the threshold value. In this case, an erroneous collision decision may be made (that is, a collision signal is erroneously outputted) despite any collision of the vehicle that does not occur, to thereby uselessly start a passenger protector.
In view of the foregoing, the present invention has been made. It is an object of the present invention to provide a collision detecting apparatus for a vehicle, which is capable of preventing the occurrence of an erroneous detection due to a periodical vibration of acceleration due to a cause other than a collision of the vehicle, thereby accurately performing a collision decision.
To achieve the above object, according to the present invention a collision detecting apparatus for a vehicle is provided including an acceleration sensor for detecting an acceleration upon collision of the vehicle, integrating means for cumulatively integrating an output from the acceleration sensor when the output exceeds a specific calculation start level and stopping the cumulative integration when the output returns to a specific calculation end level. A collision detecting means is provided for outputting a collision signal when a cumulative integral value calculated by the integrating means exceeds a threshold value. The collision detecting apparatus includes a vibration waveform detecting means for detecting that an output waveform from the acceleration sensor is a specific periodical vibration waveform, wherein when the vibration waveform detecting means detects the vibration waveform. The integrating means does not stop the cumulative integration even if the output returns to the specific calculation end level and continues the cumulative integration for the output that contains not only an output component corresponding to a negative acceleration but also an output component corresponding to a positive acceleration.
With this configuration, upon collision of the vehicle, the integrating means starts the calculation when the output from the acceleration sensor exceeds a specific calculation level, and the collision detecting means outputs a collision signal when a cumulative integral value calculated by the integrating means exceeds a threshold value. If the vibration waveform detecting means does not detect any vibration waveform when the output from the acceleration sensor returns to a specific calculation end level in a state that the cumulative integral value does not exceed the threshold value, the cumulative integration is stopped.
When the output waveform from the acceleration sensor becomes a specific periodical vibration waveform as a result of a cause other than collision, for example, riding past a stepped portion, and the vibration waveform detecting means detects the vibration waveform. The integrating means does not stop the cumulative integration even if the output from the acceleration sensor returns to the calculation end level and continues the cumulative integration for the output that contains not only an output component corresponding to a negative acceleration but also an output component corresponding to a positive acceleration. Accordingly, in each cycle of the vibration waveform, the increase in cumulative integration can be made small as mush as possible by the effect of canceling the negative acceleration component (deceleration component) by the positive acceleration component. As a result the collision decision can be carefully made, to thereby prevent the collision detecting means from outputting an unnecessary collision signal due to the vibration waveform. This is advantageous in that even if a relatively large vibration of acceleration occurs as a result of, for example, riding past a stepped portion, the collision decision can be accurately made with a high responsiveness, thereby optimally controlling a starting time of the passenger protector on the basis of the collision decision.
According to the present invention, in the case of cumulatively integrating, on the basis of a detection of the vibration waveform, the output from the acceleration sensor contains not only an output component corresponding to a negative acceleration but also a positive acceleration. The integrating means clears the cumulative integral value each time the output is switched from a value corresponding to the negative acceleration to a value corresponding to the positive acceleration. With this configuration, since in each cycle of the vibration waveform, the increase in cumulative integral value can be effectively suppressed by the above-described cumulative integral value clearing effect, the collision decision is more carefully made, to thereby prevent the collision detecting means from outputting an unnecessary collision signal due to the vibration waveform.
According to the present invention, when the output from the acceleration sensor exceeds the calculation start level and then returns to the same level within a specific time, the vibration waveform detecting means decides that the output waveform is the vibration waveform and outputs a detection signal. With this configuration, the generation of a vibration of acceleration as a result of, for example, riding past a stepped portion can be simply, accurately detected.
According to the present invention, if after the output from the acceleration sensor exceeds the calculation start level and then returns to the same level, the output does not exceeds the same level again within a specific time, the integrating means clears the cumulative integral value at that time, and stops the cumulative integration. With this configuration, the convergence of a vibration of acceleration taken as a cause of continuing the cumulative integration even after the output from the acceleration sensor returns to the calculation end level or the dissipation of noise can be accurately detected, and since the cumulative integration is stopped after the convergence of the vibration of acceleration or the dissipation of noise is detected, the operation can be rapidly returned to the usual collision monitoring operation.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.